The Gospel of Mark, our earliest gospel, shows clear signs of theological development even within its narrative. The opening verse you cite (Mark 1:1) is widely considered a later addition by scholars - some early manuscripts don't include "Son of God." More importantly, throughout Mark, Jesus consistently tells people to keep quiet about his identity (the "Messianic Secret" - Mark 1:44, 3:12, 5:43, etc.). Even after Peter's confession, Jesus "sternly orders them not to tell anyone" (8:30).
The confession before the high priest (14:61-62) comes at the very end of Mark's narrative, after Jesus's entire ministry focused not on his identity but on proclaiming the Kingdom of God. Mark's Jesus is much more interested in showing people how to live than in having them believe specific things about him.
Remember - Mark was writing 40 years after Jesus's death, trying to make sense of who Jesus was. The historical Jesus's own focus, evident in his teachings and actions, was on love, justice, and transformation - not on having people believe particular things about his identity.
Also, the term "messiah" (Hebrew: mashiach) simply meant "anointed one" in first-century Judaism, typically referring to a hoped-for political and military leader who would restore Israel's independence from Rome and reestablish the Davidic kingdom. It had nothing to do with dying for sins, being divine, or establishing a new religion. When Mark's Jewish audience heard "messiah," they would have thought "liberator" or "king," not "divine savior who dies for our sins." This dramatically different understanding of "messiah" between first-century Jews and modern conservative Christians highlights why we need to read the gospels in their historical context.
The fact that Jesus was executed by Rome for sedition - not for claiming to be divine - further shows that "messiah" had political, not theological, implications in his time. The transformation of "messiah" into its current Christian meaning happened gradually over decades after Jesus's death, particularly through Paul's writings and later Christian theology.
